Pulsed crossed-field devices



J1me 1966 J. FElNSTElN ETAL 3,255,422

PULSED CROS SED-FIELD DEVI CES Filed Aug. '7, 1962 2 Sheets-Sheet 1 DRlvR S i JOSEPH FEINSTEIN a JEROME DREXLER 1 HUNTER L. Mc. DOWELL PULSER BY jzyrzl TORNEY J1me 1966 J. FEINSTEIN ETAL 3,255,422

PULSED CROSSED-FIELD DEVICES Filed Aug. 7. 1962 2 Sheets-Sheet 2 6.3 FIG.5

INVENTORS JOSEPH FEINSTEIN JEROME DREXLER HUNT R L.Mc.DOWELL T/ ORNEY United States Patent 3,255,422 PULSED QROSSED-FIELD DEVICES Joseph Feinstein, Livingston, Jerome Drexler, New Providence, and Hunter L. McDowell, Springfield, N..I., as-

signors to S-F-D Laboratories, Inc., Union, N..I., a corporation of New Jersey Filed Aug. 7, 1962, Ser. No. 217,238 Claims. (Cl. 33043) This application is a continuation-in-part of Ser. No. 84,153 filed Jan. 23, 1961 and now abandoned.

This invention relates in general to crossed-field devices and more particularly to novel methods and means for terminating the electron RF. wave interaction in a crossed-field amplifier or oscillator operating on a cold cathode type of electron emission.

The major structural weakness and the usual source of end-of-life in magnetrons and other crossed-field devices stems from the use of a thermionic cathode and its associated heater. In crossed-field devices this problem is worse than in beam type tubes because of'the back bombardment of the cathode by electrons accelerated by the RF. field. It is known that this back bombardment produces copious secondary electron emission so that thermionic emission is not necessary for steady state operation of a crossed-field tube at high power levels once electron emission has been initiated, and it has recently been demonstrated that an R.F. input driver pulse above some particular power level is capable of starting crossedfield electronic interaction with a cold, solid metal cathode having a secondary emission ratio greater than one. This has made it possible to operate a crossed-field oscillator or magnetron on a cold cathode basis by the injection of an RF. trigger pulse into the RF. circuit of the tube. In cold cathode operated amplifiers, the input RF. signal itself serves to initiate the self-sustaining secondary emission from the cathode.

In the case of the crossed-field amplifier, a signal which it is desired to amplify is fed into the RF. circuit of the tube to establish a traveling wave of retarded phase velocity in the electron-wave interaction region. As has been indicated, the injection of this wave will be sufiicient to initiate the emission of the secondary electrons and this emission will remain continuous, without the necessity of supplying external heating power, by

back-bombarding electrons which have gained energy.

from the wave, The interacting electron stream moves with a circumferential velocity determined by the ratio of electric to magnetic field. The phase velocity of the traveling wave is approximately synchronous with this stream velocity for a wide band of frequencies so that the electrons deliver energy to input signals within this band, the amplified output signal being fed out, for example, by an output coaxial connector or waveguide.

Whereas the initiation of the RF. amplifier input signal is sufficient to trigger self-sustained secondary emission, it has been observed that termination of the input signal is not generally effective to stop secondary emissions and the tube undesirably continues to operate in an oscillatory mode. Thus, heretofore, it has been necessary in turning off this type of tube, as well as other types of crossed-field amplifiers and oscillators, to reduce the anode-cathode potential to a point at which the electron Wave interaction is terminated. However, in pulsed operation of crossed-field devices, especially at high power levels, the necessary pulsing of the anode-cathode power supply requires pulse modulators of complex and expensive design.

It is, therefore, the principal object of this invention to provide novel methods and means for interrupting the output of a crossed-field device with simple, low power, pulsed voltage sources.

Patented June 7, 1965 One feature of the present invention is the provision of a control electrode technique for interrupting operation of a crossed-field device by effecting the collection of electrons from the anode-cathode interaction space.

Another feature of the present invention is the provision of novel control electrode structures utilizing insulated cathode end hats.

Another feature of the present invention is .the provision of novel control electrode structures utilizing grid wires spaced from the surface of the cathode.

A further feature of the present invention is the provision of a novel composite structure comprising mutually insulated cathode sections and control electrode sections.

Still another feature of the present invention is the pro-' vision of a novel control electrode structure comprising a sector-shaped element insulatedly supported in a cutout portion of a cylindrical cathode.

These and other features and advantages of the present invention will become apparent upon a perusal of the specification and following drawings wherein,

FIG. 1 is a top View, partially in cross section, of a crossed-field amplifier tube in accordance with the present invention,

FIG. 2 is a cross-sectional View of FIG. 1 taken at line 2-2 in the direction of the arrows and includes a block diagram of an input pulse source,

FIG. 3 is a cross-sectional view of an alternative cathode-control electrode structure which may be utilized in the present invention,

FIG. 4 is a-top view of the structure shown in FIG. 3,

FIG. 5 is a cross-sectional view of another cathodecontrol electrode structure in accordance with the invention,

FIG. 6 is a top view of the embodiment as shown in FIG. 5,

FIG. 7 is a longitudinal cross-sectional view of still another cathode-control electrode structure in accordance with the present invention,

FIG. 8 is a fragmentary transverse cross-sectional view of a modification of the structure of FIG. 7,

FIG. 9 is an axial cross-sectional view of another form of cross-field amplifier tube in accordance with the present invention, and

FIG. 10 is a fragmentary cross-sectional view of FIG. *9 taken at line 10-10 in the direction of the arrows.

Referring now to the drawings, the illustrative embodiment of this invention depicted in FIGS. 1 and 2 comprises a cross-field forward wave amplifier having a plurality of anode .vanes 11 secured to a cylindrical located within cylindrical wall 12 to provide coupling between the serpentine line 18 and the cavity resonators 16. A pair of elongated apertures 21 and 21' are provided in anode block 14 for coupling an input R.F. wave into one end of serpentine line 18 and out of the other end through waveguides 22 and 22' and vacuum seal windows 23.

A non-thermionic cathode 24 made of, for example, beryllium copper or molybdenum is supported coaxially within the anode block 14 by means of a hollow stem 25 extending to mate with a cathode connector structure 26. Cathode 24 is bounded by end hats or control electrodes 27 adjacent its top and bottom portion, the end hats being insulated from the cathode by any desired means such as insulator rings 27'. A magnetic field is provided within interaction region 28 by means of a magnet 29 (partially shown) mating with pole pieces 29. An external power supply B provides the necessary negative DC. potential to the cathode relative to the grounded tube body and anode vanes 13.-

In operation, a voltage on the order of kv. is applied between the grounded anode and the cathode 24. A pulsed RxF. input signal on the order of 50 watts or more is fed into the input waveguide 21, 22 to initiate a traveling wave on the serpentine line 18 thereby energizing cavity resonators 16 via coupling apertures 19 to produce a slow R.F. wave of proper phase velocity for interaction with the electrons in the interaction region 28, thereby initiating the self-sustained operation of the cathode. As the wave travels clockwise about the interaction region 28, it is amplified by continuous interaction with the electrons and emerges from the output waveguides 21', 22 to an exterior utilization load (not shown).

Although the cavity-coupled serpentine line is desired as one particularly convenient anode R.F. structure, it will be understood that many other configurations for establishing the desired interacting R.F. field may be used.

In order to terminate operation of the tube simultaneously with the reduction of the RF. input signal, the insulated end hats or disc plates 27 are energized by a pulse from the relatively low power potential source 31 controlled by the pulser 32 which also controls the operation of the input R.'F. driver source 33. It has been found that a negative voltage pulse on the order of 2 kilovolts from the source 31 at the end of the on cycle of source 33 is effective in completely removing the residual oscillatory operation of the tube. This may be explained by the fact that the application of such a negative potential to the end hats 27 reduces the electric field at the cathode Z4 and hence the velocity of the electrons emitted therefrom so that the electron- Iwave interaction necessary to sustain secondary emission no longer can take place whereby the interacting electrons are rapidly collected and active operation of the tube is terminated. The end hats 27 are preferably biased negative so that when the RP. source 33 is turned on, the end hats 27 will be at the same potential as the cathode 24 whereby they perform their conventional function of axially focusing the electron stream. It has been observed, however, that the tube may be effectively cut ofi when no bias is applied, although in this case some current will be drawn by the end hats.

In order to turn the tube off with a still smaller voltage, control electrode configurations which give more control over the potential distribution in the interaction space may be utilized as illustrated by the modifications shown in FIGS. 3 through 8.

Referring now to FIGS. 3 and 4, there is shown another form of cathode structure which may be utilized in the crossed-field device of FIGS. 1 and 2. The nonthermionic cathode 34 is supported in the same manner as the cathode 24 shown in FIGS. 1 and 2. Cathode 34 is bounded by end hats 35 insulatedly secured thereto as by insulating rings 36. A plurality of spaced-apart control electrodes or grid wires 37 extend longitudinally along the periphery of the cathode 34 within longitudinal grooves or slots therein and are .connected to the end hats 35. During operation of the crossed-field device, the control electrodes 37 are preferably operated at cathode potential. Whenever it is desired to interrupt operation of the crossed-field device, a pulse is fed through lead 3-8 to the end hats 35 and the control electrodes 37. This pulse will halt operation in the same manner as explained with regard to FIGS. 1 and 2. The grid Wires need not be placed into grooves in the cathode but may extend beyond the peripheral surface of the cathode and in such case, less control voltage would be necessary. However, in this case, care must be exercised in spacing of the wires so as to avoid shorting out of the initiating RF. wave.

Referring now to FIGS. 5 and 6, there is shown another form of cathode structure which may be utilized in the present invention. The non-thermionic cathode 41 is supported coaxially within an anode block the same as cathode 27 of FIGS. 1 and 2 and is bounded by end hats 42 via insulators 43. In the present embodiment circular control electrodes or grid wires 44 are located in an insulated manner within grooves which encircle the periphery of the cathode, these electrodes 44 being supported by means of spoke members 45 and the central rod 46 which further serve as a pulse control electrode. The necessary potential is supplied to cathode 41 by a lead 47. Here, as in FIGS. 3 and 4, when it is desired to halt operation of the crossed-field device, a pulse is applied to the control electrodes.

It should be noted that the embodiment of FIG. 3 distributes the control potential from an axial wire array whereas the embodiment of FIG. 5 uses a circumferential array. Because the electron stream is revolving circumferentially, the arrangement of FIG. 3 produces more interference with normal operation than does that of FIG. 5. However, it also yields a greater degree of control in turning ofif the tube. The arrangement of FIG. 5 may also be considered as an extension of the simple end hat control electrode to a long structure for which prohibitively high voltage would be required for turn off with the end hats alone. By breaking up the structure into a group of short height axial sections, the same performance is obtained as for a single short height tube with one pair of end hats. 7

Referring now to FIG. 7, there is shown another.axial- 1y sectioned cathode structure comprising a plurality of alternating control electrode disc sections 51 and cold cathode disc sections 52 secured in stacked and mutually insulated relation. The control pulse. is applied between conductor 52 connecting together sections 52 and conductor 51' connecting together sections 51. It may be desirable in some instances to operate the separate cathode sections and/or the separate control electrodes at different relative potentials. For example, operation of the two cathode sections 52 at difference relative voltages may enable some broad-banding of the tube due to the velocity spread in the emitted electrons. A similar broad-banding is possible by using different cathodeto-anode spacingsfor the different cathode sections. The control elements 51 would not have to extend beyond the surface of the cathode elements in which case somewhat more control voltage would be required, but there would be less tendency to short out R.F. fields.

Another way to avoid shorting out the RF. fields is to serrate the control electrodes by a plurality of radial slots 54 as shown in FIG. 8. The serrations could also take the form of a plurality of spaced-apart hairpins or wires projecting from the periphery of the control electrodes. r

The discussion to this point has been directed to the application of a negative pulse to the control electrode. It has also been discovered that active operation of a cold-cathode, crossed-field tube may be terminated by the application of a positive pulse to a control electrode whereby the interacting electrons are collected directly by this electrode. This arrangement is particularly useful in tubes having long cathodes such that negative pulsing of a simple end hat structure may notpermit adequate control of the potential distribution throughout the interaction region.

FIGS. 9 and 10 show a crossed-field amplifier particularly adapted for termination by positive pulsing. Here the traveling wave anode circuit is comprised of a circular array of half-wave resonant rods 55 alternately capacitively coupled via slotted bands 56 and connected between shorting members 57 near the ends of cylindrical metal vacuum housing 58. The slow-wave structure is interrupted to provide a drift segment 59 between input coaxial line 60 and output coaxial line 61, these lines being mounted on shorting members 57 and extending axially such that the outer conductors serve as the first and last resonant rods of the slow-wave circuit and the inner conductors are connected to the adjacent resonant rods via pins 62. The axial magnetic field in the interaction region 63 is provided by coaxial solenoid 64 via annular header pole pieces 65.

The cathode assembly includes a hollow cylindrical secondary-emission cathode 66 with hollow support shaft 67 and end hats 68 connected thereto. Cathode '66 has a sector-shaped, cut-out space in which sector-shaped control electrode 69 is insulatedly disposed. Control electrode 69 is connected via cross pin 70 to support rod 71 insulatedly extending through cathode 66 and support shaft 57. Also the electrode 69 is advantageously located in the non-interacting drift region between input 60 and output 61 in order to minimize interference with the normal operation of the tube.

Operation of the tube is initiated by the introduction of the RF. input signal on input line 60 which triggers the self-sustaining emission of cathode 66, and establishes a wave on the slow-wave circuit which interacts with the electrons in interaction space 63 and emerges amplified from the output line 61. During the operating cycle the control electrode is preferably biased to the cathode potential. In order to terminate operation, a pulse (on the order of 3 kv. for an anode-cath ode voltage of kv.) is applied to electrode 69 which is positive relative to cathode 66, as indicated, in order to collect the interacting electron current.

It should be noted that according to the present invention a control electrode pulse is used to completely terminate active operation of the tube, and that during this ofi-cycle the tube may be used as a passive transmission medium or waveguide.

This invention is, of course, applicable to various known types of crossed-field devices, including, for example, those in which the slow-wave anode structure is positioned inside a hollow cylindrical cathode.

Since many changes could be made in the above construction and many apparenty widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A crossed field amplifier tube including a cylindrical cathode body portion having an emitter surface portion made from a material having a secondary emission ratio greater than 1 which enables self-sustained cold operation and also having circular end hat portions which projects over the emitter surface for inhibiting undesired cathode end current, an anode structure disposed coaxially with respect to said cathode and forming a circular re-entrant path for an electron stream from the cathode, said anode structure having formed therein a non-re-entrant slow wave circuit extending coaxially with respect to the cathode over a part-circular arc, means being provided for interrupting the slow wave circuit between the ends of the are in such a manner that wave energy propagating around said slow wave circuit does not re-enter the slow wave circuit, an input terminal for applying to the slow wave circuit R.F. wave energy to initiate self-sustained operation of said cathode, the wave energy being progressively amplified by electron interaction, an output terminal coupled to the slow wave circuit for extracting amplified energy from said circuit, one of said cathode portions forming a turn-off electrode and being insulated from the emitter surface portion of the cathode and being adapted to operate during amplification at substantially the same potential as the remainder of the cathode portions to prevent interference with normal cathode operation, the arrangement being such that the application of a suitable control voltage between the emitter surface portion of the cathode and said turnoff electrode simultaneously with the reduction of said input wave energy is elfective in rapidly terminating operation of the tube.

2. A tube according to claim 1 wherein the cathode portion forming the turn-off electrode comprises said end hat portions of the cathode.

3. A tube according to claim 1 wherein the cathode portion forming the turn-off electrode comprises a sector of said cylindrical cathode body portion.

4. A tube according to claim 1, wherein said turnoff electrode comprises a plurality of grid wires spaced from said emitter surface portion toward said anode structure.

5. A tube according to claim 4, wherein said grid wires extend between said end hat portions and are spaced from said emitter surface portion. a

6. A tube according to claim 5, wherein the grid wires are disposed in recesses in said cathode body portion.

7. A tube according to claim 4, further comprising a support rod insulatedly supported within said cathode body portion, and a plurality of spoke members radially extending from said rod member in insulated relation with respect to said cathode body portion for supporting said grid wires.

8. A tube according to claim 1, wherein said cathode body portion has a plurality of spaces formed therein, and said control turn-off electrode comprises a plurality of sections supported within said spaces.

9. A tu'be according to claim 1, wherein said cathode body portion comprises a plurality of axially spacedapart cylindrical sections, and said turn-off electrode comprises a plurality of sections intenposed between said sections.

10. A tube according to claim 9, wherein said turnoif electrode has a plurality of radially projecting serrations.

References Cited by the Examiner UNITED STATES PATENTS 2,462,137 2/1949 Smith BIS-39.63 X 2,566,087 8/1951 Lerbs 315-39.3 2,812,473 11/1957 Mourier 33043 X 2,971,121 2/1961 Dench 31539.3

ROY LAKE, Primary Examiner.

NATHAN KAUFMAN, Examiner. 

1. A CROSSED FIELD AMPLIFIER TUBE INCLUDING A CYLINDRICAL CATHODE BODY PORTION HAVING AN EMITTER SURFACE PORTION MADE FROM A MATERIAL HAVING A SECONDARY EMISSION RATIO GREATER THAN 1 WHICH ENABLES SELF-SUSTAINED COLD OPERATION AND ALSO HAVING CIRCULAR END HAT PORTIONS WHICH PROJECTS OVER THE EMITTER SURFACE FOR INHIBITING UNDESIRED CATHODE END CURRENT, AN ANODE STRUCTURE DISPOSED COAXIALLY WITH RESPECT TO SAID CATHODE AND FORMING A CIRCULAR RE-ENTRANT PATH FOR AN ELECTRON STREAM FROM THE CATHODE, SAID ANODE STRUCTURE HAVING FORMED THEREIN A NON-RE-ENTRANT SLOW WAVE CIRCUIT EXTENDING COAXIALLY WITH RESPECT OT THE CATHODE OVER A PART-CIRCULAR ARC, MEANS BEING PROVIDED FOR INTERRUPTING THE SLOW WAVE CIRCUIT BETWEEN THE ENDS OF THE ARC IN SUCH A MANNER THAT WAVE ENERGY PROPAGATING AROUND SAID SLOW WAVE CIRCUIT DOES NON RE-ENTER THE SLOW WAVE CIRCUIT, AN INPUT TERMINAL FOR APPLYING TO THE SLOW WAVE CIRCUIT R.F. WAVE ENERGY TO INITIATE SELF-SUSTAINED OPERATION OF SAID CATHODE, THE WAVE ENERGY BEING PROGRESSIVELY AMPLIFIED BY ELECTRON INTERACTION, AN OUTPUT TERMINAL COUPLED TO THE SLOW WAVE CIRCUIT FOR EXTRACTING AMPLIFIED ENERGY FROM SAID CIRCUIT, ONE OF SAID CATHODE PORTIONS FORMING A TURN-OFF ELECTRODE AND BEING INSULATED FROM THE EMITTER SURFACE PORTION OF THE CATHODE AND BEING ADAPTED TO OPERATE DURING AMPLIFICATION AT SUBSTANTIALLY THE SAME POTENTIAL AS THE REMAINDER OF THE CATHODE PORTIONS TO PREVENT INTERFERENCE WITH NORMAL CATHODE OPERATION, THE ARRANGEMENT BEING SUCH THAT THE APPLICATION OF A SUITABLE CONTROL VOLTAGE BETWEEN THE EMITTER SURFACE PORTION OF THE CATHODE AND SAID TURNOFF ELECTRODE SIMULTANEOUSLY WITH THE REDUCTION OF SAID INPUT WAVE ENERGY IS EFFECTIVE IN RAPIDLY TERMINATING OPERATION OF THE TUBE. 